CONVERSATIONS IN SCIENCE

Laser system could vaporize dangerous asteroids

Two California scientists propose a laser system that could vaporize asteroids that threaten Earth.

A time exposure from an amateur astronomer in Murrumbateman, Australia,… (Dave Herald, European Space…)

Earth dodged a gigantic space bullet Friday when the 143,000-ton asteroid known as 2012 DA14 came within 17,200 miles of the Indian Ocean. Scientists and engineers are looking for ways to head off such close calls by targeting potentially dangerous asteroids well before they're in a position to do us any harm.

A group called the B612 Foundation (a reference to the home asteroid of the Little Prince in the classic French novella)recently announced a mission to build a spacecraft that would track dangerous midsize asteroids, and a fledgling company called Deep Space Industries has floated a plan to build swarms of robots that could mine — and even destroy — space rocks.

Now, two California scientists have a new proposal to deploy an array of lasers that could vaporize asteroids from as far away as 93 million miles — the distance between Earth and the sun. Working in synchrony, the lasers could destroy a menacing asteroid outright or at least knock it off course. They call their device Directed Energy Solar Targeting of Asteroids and exploRation, or DE-STAR for short.

Philip Lubin, a cosmologist at UC Santa Barbara, and Gary Hughes, a statistician at Cal Poly San Luis Obispo, discussed their plan with The Times.

Why is it important to have a laser-shooting asteroid hunter?

Gary Hughes: There is a realistic threat of a comet or an asteroid hitting the Earth and doing untold devastation to the world. I think we should be compelled to search for realistic ways to mitigate that threat. And so that's exactly why Phil and I are so interested in this particular system.

Philip Lubin: We're trying to begin evaporating the asteroids when they're on a collision course with Earth yet still sufficiently far away to not yet be a threat. So it's sort of like a car coming at you, and you're taking some evasive action. The evasive action we're taking here is to vaporize it.

How would your device work?

Lubin: You don't blow up an asteroid like the Death Star in "Star Wars," where you push a button and the planet explodes. You basically take a blowtorch to it in the form of a laser beam and you begin to evaporate it.

The evaporation can take place over time. In our case, it takes about a few months to evaporate an asteroid the size of a few hundred meters in diameter — which is an asteroid that, if it hit the Earth, would do severe damage. The one that killed the dinosaurs was about 10,000 meters in diameter, or about 6 miles.

How hot does an asteroid have to get to evaporate?

Lubin: You have to raise the surface temperature up to above 3,000 degrees Kelvin [nearly 5,000 degrees Fahrenheit]. We can raise it to about 6,000 degrees Kelvin, which is roughly the surface temperature of the sun. When you get up to such high temperatures, all the materials that we know about essentially evaporate. So if you point this thing to a piece of concrete, the concrete will simply vaporize.

A single laser can do that?

Lubin: No. It's not sufficient to simply have a lot of power in a light beam; because of the wave-like nature of light, light will diffract in such a way that the beam will spread out. You have to focus that power in order to raise the temperature to the point at which it basically begins to boil. In order to focus a light beam over large distances, you need a large, spatially extended structure.

Can it evaporate any asteroid?

Lubin: What we're proposing is to try to go after asteroids that are about up to 500 meters in diameter by direct evaporation. For asteroids that are larger than that, what we propose is to modify their orbit by forming a jet plume on the surface using the same technique: raising the temperature, and then having that hot surface act as a rocket jet.

This sounds like science fiction. Is it possible with today's technology?

Lubin: This is not a system we can go out and build tomorrow. This is a system that's sort of on the cusp of technology at this point.

What we're proposing is to expand the existing technology. There will have to be some significant technology developments, but it doesn't need any miracles.

How does your idea stack up against the competition?

Hughes: Some of the initiatives that I've heard about are to go blasting the thing out of the sky with some sort of other weapon like a nuclear bomb, or deflect it with a bomb so that it misses the Earth. I think some of those may be viable, but I think they're also difficult.

Are there other uses for this technology?

Hughes: There's a big idea about mining rare earth elements — they're rare on Earth but enriched in things like asteroids. Everybody's trying to find new sources of these elements for things like hybrid car batteries. So a lot of people are looking at asteroids for their economic potential for just that reason. Once you vaporize the surface of an asteroid with a laser, by analyzing the absorption lines, we could tell exactly what that asteroid is made of.

Lubin: The ability to destroy asteroids is one important aspect of what we're doing, but it may not even be the most important aspect. We feel the same technology can be used to propel spacecraft into our solar system at much higher speeds than can be done with chemical propellants. We worked out the numbers and it looks like we might be able to propel a small robotic craft to Mars in a matter of a few days.